New clue found to cause of Alzheimer's

Randolph E. Schmid, Associated Press

Published
4:00 am PDT, Monday, June 23, 2008

Researchers have uncovered a new clue to the cause of Alzheimer's disease.

The brains of people with the memory-robbing form of dementia are cluttered with a plaque made up of beta-amyloid, a sticky protein. But there long has been a question whether this is a cause of the disease or a side effect. Also involved are tangles of a protein called tau; some scientists suspect this is the cause.

Now, researchers have caused Alzheimer's symptoms in rats by injecting them with one particular form of beta-amyloid. Injections with other forms of beta-amyloid did not cause the illness, which may explain why some people have beta-amyloid plaque in their brains but do not show disease symptoms.

The researchers used extracts from the brains of people who donated their bodies to medicine.

Forms of soluble beta-amyloid containing different numbers of molecules, as well as insoluble cores of the brain plaque, were injected into the brains of rats. There was no detectable effect from the insoluble plaque or the soluble one-molecule or three-molecule forms, the researchers found. But the two-molecule form of soluble beta-amyloid produced characteristics of Alzheimer's in the rats, they reported.

Morrison-Bogorad said the findings may help explain the discovery of plaque in the brains of people who do not develop dementia. For some time, doctors have wondered why they find some brains in autopsy that are heavily coated with beta-amyloid, but the person did not have Alzheimer's.

The answer may lie in the two types of beta-amyloid that did not cause symptoms. Now, the question is why one has the damaging effect and not others.